The present invention relates to a new and improved cold rolling method and cold rolling apparatus for the performance of such method.
Generally speaking, the cold rolling method is employed for fabricating, by cold working, a workpiece having straight or helical profile. The workpiece is displaced along its lengthwise axis and discontinuously rotated thereabout and externally machined by substantially ring-shaped profiled generating rolls. By means of each generating roll there is accomplished in the same and predominantly in the directional sense extending in the lengthwise direction of the profile individual generating or rolling operations which are briefly effective in rapid sequence and accommodated to the profile division and the movement of the workpiece. Thus, with the same generating roll individual rolling operations, carried out in succession, can be serially performed at a screw-line shaped region or zone of the workpiece surface which is governed by the workpiece movement, and there are performed in the profile lengthwise direction successive individual rolling operations which, as concerns their effect at the workpiece, overlap.
Generally speaking, the cold rolling machine for performance of the method is of the type comprising at least one revolvingly driven generating or rolling head in which there is rotatably mounted at least one generating roll and, further, possesses synchronized drives for the generating or rolling heads and the workpiece.
A similar method and cold rolling machine, employing continuous or intermittent rotational drive of the workpiece, is disclosed in German Pat. No. 1,016,222. With the continuous drive mode of operation, the workpiece also rotates during such time as the generating rolls are in engagement therewith. With the intermittent drive mode of operation, the rotational movement of the workpiece is stopped during such time as the generating rolls are in engagement with the workpiece.
The continuous drive mode affords the advantage that there are possible large angular velocities, because there do not occur any mass acceleration forces. Furthermore, an advantageous aspect thereof is the possibility of being able to change the number of teeth to be formed at the workpiece by simply changing change gears. What is however disadvantageous is the accuracy which can be attained with this operation, frequently not always adequate, because there occurs an undesired generating movement between the workpiece and the generating roll.
With the intermittent drive mode, by means of a Maltese cross-like mechanism, there is available the advantage that, owing to the standstill of the workpiece during such time as the generating rolls are effective thereat, there can be realized extremely great machining accuracy. On the other hand, what is however disadvantageous is that high mass acceleration forces prevail due to the unfavorable course of the velocity, and therefore, there are only possible low velocities. Additionally, the extreme accuracy can only be obtained if there is employed, for each tooth number, a specially designed Maltese-cross-like partial plate, which, however, is expensive and the exchange of which is time-consuming.